OBD-II is a system used in automobiles to monitor various components of the vehicle, detect malfunctions, and store the information in the vehicle s on-board computer to be recovered later by a service technician. OBD-II is an acronym for on-board diagnostics; the II denotes the second and most current version of this technology. Beginning in the late 1970s, vehicles sold in the United States have been equipped with electronics to control various systems and diagnose malfunctions with the goal of minimizing pollution. This came about in response to Congress passing the Clean Air Act and establishing the Environmental Protection Agency (EPA) in 1970. These electronics varied between manufacturers and model years, making the retrieval of diagnostic information potentially costly and time-consuming.

In 1988, the EPA and California s Air Resources Board (CARB) mandated that vehicle manufacturers include self-diagnosing programs to ensure that their emissions equipment would remain effective for the vehicle s service life. The Society of Automotive Engineers standardized a connector plug and a set of diagnostic test signals. Upon equipment failure, this system illuminated a malfunction indicator light (MIL) on the vehicle s dashboard, often called the check engine light. This system, required in all 1991 and newer automobiles, became known as on-board diagnostics I, or OBD-I.